Mold press

ABSTRACT

An apparatus for molding plastics is provided with an elastic member adapted to press a mold top against a mold bottom and with a tie-rod assembly adapted to alternately move the elastic member from the mold top and to position it over the mold bottom without change in the pressure exerted by the elastic member against the mold top.

1451 Sept. 25, 1973 [22] Filed:

[ 1 MOLD PRESS [76] Inventor: Carlo F. Tondato, Strado San Vincenzo40.10, Torino, Italy Nov. 18, 1970 1211 Appl. No.: 90,498

[30] Foreign Application Priority Data Oct. 24, 1969 Italy 53811 A/69 52us. (:1 425/193, 425/406, 100/268 511 1111.01. B296 3/00 58 Field 61Search 18/16 R, 16 11; 100/214, 268; 425/193, 406, 410

[56] g I References-Cited UNITED STATES PATENTS 1,383,748 7/1921 Olsonet a1 425/195 X 2,103,951 12 1937 Lewis..... 425/195 2,559,478 7/1951Stone 173/119 2,602,507 7/1952 Adams 173/119 X COllel 173/119 1,006,87310/1911 Phillips 173/120 2,815,551 12/1957 Hessenberg et a1... 164/833,667,536 6/1972 Colombo 164/83 X 3,209,057 9/1965 Lassman 18/16 R X64,584 5/1867 Schubeus... 100/214 X 1,174,646 3/1916 Williams 18/16 R X2,869,173 l/1959 Van Hartesveldt et al 18/16 H 2,979,770 4/1961 Greeneet a1. 18/16 R X 3,602,948 9/1971 Lejeune 18/16 H X PrimaryExaminer-Robert L. Spicer, Jr. Att0rneyClelle W. Upchurch [5 7] ABSTRACTAn apparatus formolding plastics is provided with an elastic memberadapted to press a mold top against a mold bottom and with a tie-rodassembly adapted to al- Claims, 2 Drawing Figures ...a va

MOLD PRESS This invention relates to a method of and an apparatus forpressing together die parts or like tools, particularly in themanufacture of articles from natural and synthetic resins or plastics,particularly from rubber or elastomers, preferably having a cellularstructure.

For the moulding of articles of rubber or elastomers use is made ofdevices comprising a stationary lower die and a vertically movable upperdie. The vertical movability of the upper die makes it possible for thematerial from which the articles are to be moulded and which, forexample is to be shaped by the action of heat and/or pressure, to beinserted into the die cavity, and subsequently enables the mouldedarticle to be removed from the die. Pressing devices are necessary topress the two parts of the die together.

In known pressing devices the upper and lower dies are pressed togetherby fastening the upper die part to the piston rod of a double actinghydraulic or pneumatic piston-cylinder assembly. The force by means ofwhich the two parts of the die are pressed together is directlyproportional to the pressure of the hydraulic or pneumatic medium. Thehydraulic or pneumatic pressure medium is usually taken from a centralsupply system, in which fluctuations in pressure frequently occur. Inconsequence of these pressure fluctuations considerable pressing defectsoccur in the pressing-together of the die parts. In order to obviatethis disadvantage it is conceivable for each pressing device to beprovided with its own pressure medium supply system. The cost ofpurchasing such pressing device would then, however, be very high.

The invention aims at providing a simple, economical method andapparatus for pressing together die parts or like tools, which is freefrom the disadvantages of known pressing devices.

Accordingly, the present invention consists in a method of pressingtogether die parts or like tools, particularly in the manufacture ofobjects from natural and synthetic resins or plastics, especially rubberor elastomers, preferably having a cellular structure, character'- isedin that the pressing-together of the die parts is effected by apre-stressing force, corresponding to the desired pressing force, withthe aid of elastic means which act on at least one of the die parts,while. through further stressing of the elastic means oppositely to theclosing direction of the die parts the pressing force is relieved.

Thus, the invention ensures in a very simple and reliable manner thatthe die parts will be pressed together with exactly the desired force,that is a predetermined spring force. On completion of the pressingoperation the pressing force is relieved again in a very simple manner.

The most diverse forms of apparatus can be used for carrying out themethod of the invention. A particularly advantageous apparatus ischaracterised by at least one pre-stressed coil compression spring whichis supported at its one end against the upper die part and at its otherend against a plate fixedly mounted above said upper die part. Theaccurately pre-stressed coil compression spring thus applies the desiredpressing pressure to the two die parts with the greatest reliability.

For the exact adjustment of the desired pre-stressing of the spring saidplate is displaceable in the direction of the axis of the spring bymeans of a screwthreaded spindle which carries said plate. The desiredprestressing force can thus be adjusted in a very simple manner at anytime and very quickly.

In respect of the relieving of the pressing force on completion of thepressing operation there are two particularly convenient possibleconstructions for the pressing apparatus.

In one case the coil compression spring may be supported directlyagainst the upper die part while the pressing force can be relieved byraising the latter. This construction is intended particularly for dieswhich remain at least partly in the pressing apparatus.

In the second case the coil compression spring may be supported againstthe upper die part with the interposition of a movable plate unconnectedto the upper die part, in which case the pressing force can be relievedby raising the movable plate. This arrangement is particularly suitablefor dies passing through the pressing apparatus.

In both cases a single-acting pressure cylinder together with tie rodsconnected by a cross-bar may be provided for raising the upper die partor the movable plate.

The increase of the stressing of the coil compression spring, which iseffected on the raising of the upper die part or of the movable plate,has the additional consequence that the next pressing operation isinitiated automatically and at very high speed as soon as no pressuremedium is active in the pressure cylinder.

It should be added that mould parts may also advantageously replace thedie parts.

In order that the invention may be more readily understood, reference ismade to the accompanying drawings which illustrate diagrammatically andby way of example, two embodiments thereof, and in which:

FIG. 1 is an elevation of an apparatus according to the invention forpressing together die parts connected to the pressing apparatus, and

FIG. 2 illustrates a similar device for pressing together die partswhich are not connected to the pressing apparatus, that is which areremovable from the apparatus.

Referring to FIG. 1 of the drawings, a lower die 5, which co-operateswith an upper die 6, is fast with the base 1 of a frame 1, 2, 3 and 4.The upper and lower dies 6, 5 enclose a cavity for receiving a materialwhich is to be maintained under pressure, that is moulded into anarticle.

The upper die 6 is urged against the lower die 5 by the action of a coilcompression spring 7 disposed between the upper die 6 and a plate 8fixedly mounted at 7 one end of a screwthreaded spindle 9 which at itsother end is screwed into the transverse bearer 4 of the frame. Duringthe pressing operation the coil compression spring 7 is continuouslysubjected to pre-stressing, the magnitude of which can be varied byrotating the plate 8 and consequently the spindle 9 by means of its Theupper die 6 is thereby lifted off the bottom die by means of the tierods and 11, so that the die cavity is freely accessible. At the sametime the stressing of the coil compression spring 7 is increased, whichhas the consequence that the next closing of the pressing apparatus isinitiated automatically and at high speed as soon as no pressure mediumis acting in the cylinder 14.

The apparatus illustrated in FIG. 2 serves for pressing together dieparts 5a and 6a which are not connected to the pressing device. As canbe seen from the drawing, in this apparatus the tie rods 10a and 11a arenot fastened to the top die part 6a but to a plate 16 which is notconnected to the upper die part 6a. In other respects the constructionand mode of operation of this apparatus corresponds to the embodimentillustrated in HO. 1.

The devices described above can be varied in different ways. Forexample, the coil spring 7 can be replaced by a pneumatic dash potassembly and the pressure cylinder 14 by a motor of another kind, forexample a linear electromagnetic motor or by a lifting mechanism whichcan be operated by a conventional electric motor or optionally also byhand. The Medic parts 5, 6 and 5a, 6a can similarly be replaced by mouldparts.

I claim:

1. An apparatus for molding plastics comprising a die having a cavitatedbase and a lid separable therefrom, means for pressing the lid againstthe base comprising a spring compressed between the lid and a rigidbackup plate spaced above the lid, and means for lifting the lid fromthe base and for compressing the spring comprising a pair of tie rodssecured at one end to the lid and at the other end to a cross-bar abovethe spring, a hydraulic cylinder having a piston therein and a pistonrod secured to the cross-bar, means for charging fluid under pressureinto the cylinder to actuate the piston and to lift the cross-bar, andmeans for releasing the fluid from the cylinder, whereby upon the saidrelease of fluid the compressed spring presses the lid against the base.

2. An apparatus for molding plastics comprising a die having a cavitatedbase and a lid separable therefrom, means for pressing the lid againstthe base comprising a separable plate disposed on the lid and a springcompressed between the plate and a rigid back-up plate spaced above theseparable plate and means for lifting the plate from the lid and forreleasing the springs pressure from the lid comprising a pair of tierods secured at one end to the separable plate and at the other end to across-bar disposed above the spring, a hydraulic cylinder having apiston therein and a piston rod secured to the cross-bar, means forcharging fluid under pressure into the cylinder to actuate the pistonand to lift the cross-bar, and means for releasing the fluid from thecylinder, whereby upon the said release of fluid the compressed springpresses the separable plate against the lid and presses the lid againstthe base.

3. An apparatus for molding plastics comprising a die having a cavitatedbase and a lid separable therefrom, means for pressing the lid againstthe base comprising a spring, and means for compressing the spring andthereby release the lid comprising a hydraulic cylinder having a pistontherein, means for charging fluid under pressure into the cylinder toactuate the piston and compress the spring, and means for releasing thefluid from the cylinder whereby upon release of the fluid the spring isreleased and presses the lid against the base.

4. An apparatus for molding plastics comprising a die having a cavitatedbase and a lid separable therefrom, means for pressing the lid againstthe base comprising a spring, and means for lifting the lid from thebase and for compressing the spring comprising a pair of tie-rodssecured at one end to the lid, a hydraulic cylinder having a pistontherein and a piston rod secured to the tierods, means for chargingfluid under pressure into the cylinder to actuate the piston and to liftthe tie-rods, and means for releasing the fluid from the cylinder,whereby upon the release of the fluid the compressed spring presses thelid against the base.

1. An apparatus for molding plastics comprising a die having a cavitatedbase and a lid separable therefrom, means for pressing the lid againstthe base comprising a spring compressed between the lid and a rigidback-up plate spaced above the lid, and means for lifting the lid fromthe base and for compressing the spring comprising a pair of tie rodssecured at one end to the lid and at the other end to a cross-bar abovethe spring, a hydraulic cylinder having a piston therein and a pistonrod secured to the cross-bar, means for charging fluid under pressureinto the cylinder to actuate the piston and to lift the cross-bar, andmeans for releasing the fluid from the cylinder, whereby upon the saidrelease of fluid the compressed spring presses the lid against the base.2. An apparatus for molding plastics comprising a die having a cavitatedbase and a lid separable therefrom, means for pressing the lid againstthe base comprising a separable plate disposed on the lid and a springcompressed between the plate and a rigid back-up plate spaced above theseparable plate and means for lifting the plate from the lid and forreleasing the spring''s pressure from the lid comprising a pair of tierods secured at one end to the separable plate and at the other end to across-bar disposed above the spring, a hydraulic cylinder having apiston therein and a piston rod secured to the cross-bar, means forcharging fluid under pressure into the cylinder to actuate the pistonand to lift the cross-bar, and means for releasing the fluid from thecylinder, whereby upon the said release of fluid the compressed springpresses the separable plate against the lid and presses the lid againstthe base.
 3. An apparatus for molding plastics comprising a die having acavitated base and a lid separable therefrom, means for pressing the lidagainst the base comprising a spring, and means for compressing thespring and thereby release the lid comprising a hydraulic cylinderhaving a piston therein, means for charging fluid under pressure intothe cylinder to actuate the piston and compress the spring, and meansfor releasing the fluid from the cylinder whereby upon release of thefluid the spring is released and presses the lid against the base.
 4. Anapparatus for molding plastics comprising a die having a cavitated baseand a lid separable therefrom, means for pressing the lid against thebase comprising a spring, and means for lifting the lid from the baseand for compressing the spring comprising a pair of tie-rods secured atone end to the lid, a hydraulic cylinder having a piston therein and apiston rod secured to the tie-rods, means for charging fluid underpressure into the cylinder to actuate the piston and to lift thetie-rods, and means for releasing the fluid from the cylinder, wherebyupon the release of the fluid the compressed spring presses the lidagainst the base.